1. Field of the Invention
This invention relates to Private Branch Exchange (PBX) switching systems and, in particular, to circuitry for providing an executive ringback feature.
2. Description of the Prior Art
In prior art PBX systems the ability of a calling party to be rung back after placing a call to a busy called party required the calling party, upon receipt of a busy tone, either to hang up and then dial a special ringback code followed by the directory number of the busy called party or to flash his switchhook and then dial in a time code when callback was to be attempted. One of the disadvantages in implementing executive ringback in accordance with the first approach is that the calling party must first hang up upon receipt of the busy tone. Another disadvantage is that special circuitry must be provided in the PBX system to recognize the special code required to initiate an executive ringback sequence. A third disadvantage is that the calling party must redial the directory number of the busy called party once the PBX system has been alerted that an executive ringback request has been made. A disadvantage with the second approach is that the called party may have completed his conversation with the third party a substantial time period prior to ringback and, as a result, he may no longer be in the area of his station set. Hence, although ringback is implemented it is of little utility. These disadvantages make the provision of executive ringback expensive in both the amount of time required to effect a ringback and in the amount of equipment needed to supply this feature, and, also, limit the utility of such a service.
Accordingly, it is one object of the present invention to reduce the amount of time expended by a calling party in effecting an executive ringback function.
Another object is to eliminate the need for the calling party to redial the directory number of the busy called party.
A further object of the present invention is to reduce the amount of PBX system equipment required to provide an executive ringback feature.
Yet another object is to eliminate the need for the calling party to first hang up and then dial a special executive ringback code.
Still another object of the present invention is to effect the ringback immediately upon the called station going idle after completion of the conversation with the third party.